Hydrogen is used in petroleum refineries to remove sulfur from fuel products and to saturate olefins and aromatics to make chemical products. Hydrogen is produced as a byproduct in petroleum refineries and petrochemical plants. Byproduct hydrogen collects in light ends streams containing light hydrocarbons and also non-condensable gases—including carbon monoxide, carbon dioxide, and nitrogen. The light ends streams are usually processed to recover propane, propylene and heavier hydrocarbons using conventional fractionation techniques at ambient temperatures, and then further processed to recover ethylene, ethane and hydrogen at cryogenic temperatures. Streams processed at low temperatures are usually dried to remove water and treated to remove corrosive compounds including hydrogen cyanide, hydrogen sulfide, and also carbon dioxide.
Demand for hydrogen in petroleum refineries is increasing because allowable sulfur levels in fuels are being reduced particularly for heavier fuels. Also, increasing desulfurization intensity generally requires purer hydrogen which is taxing current hydrogen recovery processes. In most refining and petrochemical sites recovered byproduct hydrogen is not adequate to meet demand. Refiners make up the hydrogen shortfall by manufacturing on purpose hydrogen via steam reforming methane, propane, and naphtha. Unfortunately, on purpose hydrogen costs about three times as much as recovered byproduct hydrogen and also releases carbon dioxide into the environment.
With current technology typically only about 50% of the byproduct hydrogen produced in light ends streams is recovered. Hydrogen not recovered ends up in fuel gas streams and is burned. A primary reason why hydrogen recovery rates are low with current technology is that hydrogen bearing light ends streams usually contain non-condensable gases—nitrogen and carbon monoxide—and these gases are difficult to separate from hydrogen with current technology.
Hydrogen bearing light ends streams produced in petroleum refineries and petrochemical plants include off gas streams from fluid catalytic crackers, cokers, crude oil fractionation, isomerization, desulfurization, hydrocrackers, and dealkylation.
There is a need for a new process that can be readily integrated into refineries and petrochemical plants that recovers hydrogen produced in light ends streams to high yield and purity. The process of the present invention answers this need: it recovers up to 97% of the hydrogen available in light ends streams, including streams containing non-condensable gases such as nitrogen and carbon monoxide and can produce product hydrogen at purities of 98 mole % or higher, at a cost one third of on purpose hydrogen.